A transport device for developing powder

Abstract: A transport device for supplying developing powder from a lower-level reservoir (1) to a developing station by means of a rotatable spiral spring (13) contained in a transport tube (10). The transport tube has an inlet aperture (21) near the lowest point of the reservoir (1). Together with the spiral spring (13), blades (23, 24) rotate around the inlet aperture (21) provided with an inlet blade (22) to push developing powder in the transport tube (10) in order thus to ensure upwards transport of developing powder even in the event of a low level in the tube. A low-level detection element (32) is coupled to the rotating blades (23, 24) to prevent the conveyor pipe emptying and a pipeline effect occurring as a result of the developing powder in the reservoir running out.

Description: The invention relates to a device for transporting developing powder from a reservoir to a developing station, comprising a tube provided with an inlet aperture at the reservoir and an outflow aperture at the developing station, said outflow aperture in the operative state being at a higher level than the inlet aperture, and a helical transport means disposed in the tube and rotatable about its longitudinal axis, which transport means, on rotation, can feed developing powder from the inlet aperture to the outflow aperture. A device of this kind is known from EP-A-0 256 862. In this known device, for transporting magnetic developing powder from a lower-level reservoir to a higher-level developing station, magnetic means are provided which pull against the tube wall powder particles for transport through the tube, in order thus to allow powder transport in the upward direction in the tube by means of a helical transport means. One disadvantage of this method of raising developing powder is the presence of magnets formed around the tube, such magnets requiring a complex construction adapted to the tube shape. Another objection is that the known device is only usable for raising developing powder having magnetic properties. The object of the invention is to provide a transport means for raising developing powder without these disadvantages. To this end, according to the invention, in a device according to the preamble, the inlet aperture is formed in a lower end of a wall part of the tube and a pushing means is provided in the reservoir comprising at least one blade rotatable about the rotational axis of the transport means and installed at the same height as the inlet aperture for pushing developing powder present in the reservoir through the inlet aperture in the tube. Consequently, to raise developing powder a powder transport device is provided which requires no adaptation to the transport tube and leaves the outside of the latter fee, said device also being usable for raising non-magnetic developing powder by means of a conveyor screw. In EP-A-0 462 912 a device is shown for transporting powder out of a reservoir via a tube put into the reservoir, the tube having an inlet aperture formed by a hole in a wall part of the tube. This known device is provided with a rotatable blade positioned below that inlet aperture, so being less effective as a device according to the present invention wherein the rotatable blade is level with the inlet opening in the tube. In one advantageous embodiment of a device according to the invention, the at least one blade forms an obtuse angle α with a radial plane through the rotational axis intersecting the blade edge closest to the rotational axis. In another or further attractive embodiment of a device according to the invention, the inlet aperture lies in a plane forming an acute angle β with a radial plane through the rotational axis which intersects the edge of the inlet aperture furthest away from the rotational axis. This attractive embodiment or these attractive embodiments are a simple way of ensuring that there is sufficient flow of developing powder to the inlet aperture of the tube, even in the event of a low level in the reservoir, in order to ensure upwards transport of developing powder through the tube. Other features and advantages of the invention will be explained hereinafter with reference to the accompanying drawings wherein: Fig. 1 is a cross-section of the device according to the invention. Fig. 2 is a cross-section on the line II-II in Fig. 1, and Fig. 3 graphically shows the relationship between the quantity of developing powder transportable through the tube per unit of time with the device shown in Figs. 1 and 2, and the level in the reservoir. The device shown in Fig. 1 comprises a cylindrical reservoir 1 with a vertical cylinder axis, the top of the reservoir 1 being provided with a closable filling aperture 2 for filling the reservoir 1 with developing powder from a transport packing (not shown), e.g. a top-up bottle. Taking as a basis a top-up bottle which can contain 400 grams of developing powder, which quantity must be capable of introduction into the reservoir in one operation, and in the event of residual powder left in the reservoir being 100 grams, the reservoir must be capable of taking a total of 500 grams of developing powder. The volume of the reservoir is derived from the specific gravity of loosened (aerated) developing powder, which is for example 0.3 kg/dm 3 . In the case of the reservoir shown in Fig. 1, its height is approximately equal to its diameter. The upright cylindrical reservoir 1 is fixed by a strap 3 in an electrophotographic copier, which is otherwise not shown, at a place which can be distant from the developing device contained therein. The reservoir 1 has a conical base 4 provided with a shaft bushing 5 along the cylinder axis. A shaft 6 is mounted in the shaft bushing 5 and outside the reservoir 1 is coupled to a drive (not shown) while inside the reservoir 1 it has an axle stub 7, to which elements movable in the reservoir are fixed, as will be described hereinafter. A transport tube 10 of round cross-section is fixed in the reservoir 1 and extends therein from the axle stub 7, around which the tube end 11 fits with ample clearance, and from there extends upwards, straight at first, through the reservoir and then with an ample bend to outside the reservoir. The following part 12 of the transport tube outside the reservoir 1, which may be flexible to some extent, extends horizontally to the developing device of the copier, in which developing device the transport tube leads into a powder mixing section where supplied developing powder is mixed with the developing powder still present. A spiral powder transport spring 13 is disposed in the transport tube 10. The coils of the spring 13 fit with slight clearance inside the tube 10. One end of the spring 13 drops around the axle stub 7 and is rigidly secured to a rotor 14 fixed on the shaft 6. Rotor 14 carries elements for loosening and keeping in a free-flowing form the developing powder present in the reservoir, and elements to promote the flow of developing powder to the lowest part of the reservoir 1 and thus prevent compacting and bridge formation of developing powder in the reservoir. An L-shaped agitator bar 18 forming part of the rotor 14 rotatable around the transport tube 10 serves to keep the powder free-flowing. To prevent bridge formation a 1 mm thick wire 19 is used, which also forms part of the rotor 14 rotatable about the transport tube 10 and which moves at a distance of 2 mm along the side wall of the reservoir, i.e. without making contact therewith, in order to prevent powder from caking against the wall. At the part of the transport spring 13 situated around the axle stub 7 the transport tube 10 is provided with a funnel-shaped inflow aperture 21, the top edge of which is lower than the top of the axle stub 7. The funnel-shaped opening 21, as shown in Fig. 2, is made by a break in the tube wall over a quarter of the cylindrical tube periphery and the formation of a flat blade 22 which extends from one side of the break tangentially outwards over a distance equal to the radius of the outside cross-section of the transport tube 10. A funnel-shaped inflow aperture is thus formed with an outermost inflow plane including an angle β of 45° with a radial plane passing through the outermost edge of the flat blade 22. Two diametrically opposite blades 23 and 24 are disposed on the rotor 14, level with the funnel-shaped aperture 21, and each forms an angle α of 110° with a radial plane passing through the edge of the blade closest to the centre of the reservoir 1. The angles α and β can vary within specific limits without affecting their proper operation, e.g. within limits of ± 15°. On rotation of the rotor 14, the operative surfaces of the blades 23 and 24 thus each exert an inwardly directed force on the developing powder to press the powder into the inlet aperture 21 of the transport tube 10 to the bottom coils of the transport spring 13, which carry the powder on up through the transport tube 10. The pushing produced by the blades 22, 23 and 24 ensures that even if the level in the reservoir is low sufficient powder transport is maintained through the transport tube 10. The operation of the device will now be described further with reference to Fig. 3. A test rig was made with a 305 mm long transport tube 10 having an inside diameter of 15 mm. The transport tube had an approximately 150 mm long vertical part, a bend with an inside radius of 50 mm, and a horizontal part approximately 80 mm long provided with an outflow aperture 12. The inlet aperture 21 in the bottom part 11 of the transport tube 10 had a height of 10 mm and the axle stub 7 projected a distance of 15 mm into the transport tube 10. A transport spring 13 made of 0.5 mm thick spring steel was disposed in the transport tube 10 and had an outside diameter of 13 mm, an inside diameter of 9 mm and a pitch of 5 mm. With this test rig, and a speed of rotation of 35 rpm for rotor 14, a maximum rate of flow V of 4 g per min. was measured when the reservoir 1 was completely full and 0 grams developing powder discharged. When 430 grams of developing powder had been discharged and the reservoir filled with 500 grams was thus almost empty, the measured rate of flow (V) dropped to about 2.5 g per min. In Fig. 3, line 35 denotes the value of the measured rate of flow (V) against the quantity of developing powder discharged (Q). After the powder transport device was started with reservoir 1 full and transport tube 10 still empty, it was some time before developing powder left the transport tube 10 (about 4 minutes in the test rig). In order to prevent the transport tube 10 from also becoming empty in the event of the reservoir 1 emptying, a signal to replenish the reservoir 1 is given when there is still a residual supply, for example, of 100 grams present and the transport device is rendered inoperative until the reservoir has been replenished. This avoids any pipeline effect in the transport tube and also has the effect that the spread of the rate of flow V in dependence on the degree of filling of the reservoir 1 remains restricted. On stoppage of the rotor 1 after delivery of about 400 grams of developing powder from a reservoir 1 filled with 500 grams of developing powder, the drop in the rate of flow Q is restricted to about 3 g per min. as shown by line 36 in Fig. 3. A vane 30 is disposed to be freely pivotable on the horizontal part of the L-shaped bar 18 for detection of the residual supply. When the reservoir is full, vane 30 is pressed into a horizontal position by developing powder flowing along the rotating vane. When the powder level drops below vane 30 the vane turns down to a freely hanging position shown in Fig. 1, in which position a magnet 32 fixed on the vane comes within the range of a minimum supply detector 31, e.g. a reed contact, once per revolution of the rotor 14 to deliver a low level pulse. On delivery of, for example, three consecutive low-level pulses, a minimum supply signal is delivered, the purpose of this being to exclude instability in the measurement. Since the powder transport device is rendered inoperative on delivery of a minimum supply detection signal and the vane 30 accordingly would remain in its freely hanging position even after the reservoir had been replenished, on the next activation of the copier of which the developing station forms part, the rotor 14 is rotated three times. If, on the third revolution, magnet 32 on vane 30 comes out of the range of the reed contact, it forms a signal that the reservoir is replenished up and accordingly the powder transport device is rendered operative. With the test rig it was found that without active pushing of developing powder the rate of transport V was reduced to practically zero even before a residual supply of 100 grams of developing powder in the reservoir 1 was reached, as indicated by line 37 for example. A prediction within certain limits of the quantity of developing powder leaving the reservoir 1 per unit of time is important so that when the quantity of developing powder present in the developing device (not shown) drops below a predetermined level (e.g.,in the case of a binary developing system, the fall in the concentration of developing powder in a mixture with carrier particles), approximately the same quantity of developing powder can be metered over a fixed metering period, so that in all cases approximately the same time elapses before the quantity of developing powder in the developing device is once again at the correct level. When the transport tube 10 is filled with developing powder for the first time, the cylindrical part inside the transport spring 13 in the vertical part of the spring will fill with developing powder which drops off the rotating spring coils. The axle stub 7 prevents this powder from dropping back into the reservoir 1. After the said space inside the spring is filled, the rate of transport is determined by the space between the spring coils. At that rate of transport the powder in the transport tube in the horizontal part will be located substantially in the bottom half of the transport tube where the powder is pushed in front by the spring coils without appreciable turbulence until it drops into the developing device from the transport tube at the end 12. The relatively narrow passage between the tube wall and the axle stub 7 limits the conveying capacity of the transport spring 13 so that at a required rate of transport of, for example, from 3 to 4 grams per minute, the number of revolutions of the transport spring does not become so low that the transport behaviour is irregular.

Claims: A device for transporting developing powder from a reservoir (1) to a developing station, comprising a tube (10) provided with an inlet aperture (21) at the reservoir (1) and an outflow aperture (12) at the developing station, said outflow aperture (12) in the operative state being at a higher level than the inlet aperture (21), and a helical transport means (13) disposed in the tube (10) and rotatable about is longitudinal axis, which transport means, on rotation, feeds developing powder from the inlet aperture (21) to the outflow aperture (12), characterised in that the inlet aperture (21) is formed in a lower end of a wall part of the tube (10) and in that a pushing means (22-24) is provided in the reservoir comprising at least one blade (23, 24) rotatable about the rotational axis of the transport means (13) and installed at the same height as the inlet aperture (21) for pushing developing powder present in the reservoir (1) through the inlet aperture (21) in the tube (10). A device according to claim 1, characterised in that the at least one blade (23, 24) forms an obtuse angel (a) with a radial plane through the rotational axis intersecting the blade edge closest to the rotational axis. A device according to claim 2, characterised in that the obtuse angle (α) is between 95° and 125°. A device according to claim 2 or 3, characterised in that two diametrically opposite blades (23, 24) are provided. A device according to any one of claims 1 to 4, characterised in that the inlet aperture (21) lies in a plane forming an acute angle (β) with a radial plane through the rotational axis which intersects the edge of the inlet aperture (21) furthest away from the rotational axis. A device according to claim 5, characterised in that the acute angle (β) is between 30° and 60°. A device according to claims 2 and 5, characterised in that the edge of the blade (23, 24) closest to the rotational axis and the edge of the inlet aperture (21) furthest away from the rotational axis are situated in substantially the same peripheral plane with respect to the rotational axis. A device according to any one of the preceding claims, characterised in that the helical transport means is a spiral spring (13), one end of which extends substantially to the lowest point of the tube and in that an axle stub (7) at said end extends coaxially and so as to fit into the spiral spring over a distance which at least extends over the dimension of the inlet aperture (21) in said direction. A device according to any one of the preceding claims, characterised in that the pushing means (23, 24) disposed outside the tube (10) and the transport means (13) disposed inside the tube are rigidly interconnected for common drive purposes. A device according to any one of the preceding claims, characterised in that the pushing means (14, 23, 24) carries an arm (18) which extends in the horizontal direction in the reservoir and around which a vane (30) is disposed to pivot freely and, on operation of the pushing means (14, 23, 24) and when the supply of developing powder in the reservoir (1) is larger than a minimum supply, is pushed by the developing powder into a position other than the vertical and, when there is a minimum supply of developing powder, hangs freely down so that the vane (30) comes within the range of a minimum-supply detector (31).

Inventors: VOLLENBROEK ROBERTUS MARIA, VOLLENBROEK, ROBERTUS MARIA
Applicants: OCE TECH BV, OCE-TECHNOLOGIES B.V.
Application year: 1994
Main classification: G03G15
IPC codes: G03G15, B65G65